The invention relates to the making and breaking of connections between pipe sections and a pipe string projecting from a drilling rig in a bore hole in the lithosphere, for instance in the course of drilling or lining oil or gas wells.
Drilling for oil or gas and lining of the well typically involves the introduction of a large number of pipe sections or stands such as drill pipe sections and casing pipe sections into the well. The sections are each time connected to a string of sections projecting into the well after having been brought into line with the pipe string. Each section may be formed by a single joint or by a plurality of joints which have been connected to each other before being connected to the string.
During drilling, the string is typically rotated while mud is being fed to the string for instance to drive a mud motor of a drill bit at the extreme end of the string. Mud can also be fed to facilitate introduction of the string into the bore hole. It is also known to rotate a casing string during insertion into a bore hole.
Couplings between successive pipe sections are typically made or undone by screwing the pipe sections onto the string or unscrewing the pipe sections from the string. To reduce the number of rotations requires to make or break a connection, the mating threads of the couplings are usually of a generally conical shape. The spinning of each section to be connected or removed is typically carried out after having stopped rotation of the string. Tongs such as Wheatherford tongs or a so-called Iron Roughneck are used to spin each pipe section to be connected and to exert the final or initial torque required to make or, respectively, break the connection.
The efficiency and effectivity of such operations is substantially impaired by the interruption of the drilling or lining process required to connect or disconnect the next section. This is of particular importance, because the drilling of a bore hole typically involves a plurality of tripping operations (extracting and re-introducing the string) for inspection and/or replacement of the drill bit. Each tripping operation includes the disconnection and connection of about 50-300 sections. More specifically, stopping the rotation of the string has various adverse effects; such as unwinding if the pipe string is a drill string. After rotation of a drill string has been restarted, it typically takes 10-30 minutes before a reasonably stable operating equilibrium is reached. Moreover, stopping rotation of a string in a bore hole increases the risk of the string getting stuck in the bore hole. As such, the period between stopping the string and restarting the string adds to the time required to couple or remove a pipe section as well.
It is known from U.S. Pat. No. 3,708,020 to Adamson to keep a small drill string for taking cores of geological formations or concrete rotating while drill pipe connections are made or released. However, the exertion of torques to make or break the connections between successive lengths of drill pipe disturbs the operating equilibrium of the rotating drill string, which adversely affects the rate of progress and the tool life of the drill bit.
It is an object of the present invention to provide a possibility to reduce the time required to add or remove pipe string sections and to allow the connection between successive sections of the pipe string to be made while substantially reducing the extent to which the operating equilibrium of a rotating string in a bore hole is disturbed.
According to the present invention, this object is achieved by providing a method for making or breaking a coupling between a pipe section and a pipe string projecting from a rotary drilling rig into a bore hole in the lithosphere, in which the pipe section is rotated relative to the pipe string by applying a torque up to a make-up or breaking torque, exertion of that torque generates a reactive torque in an opposite sense of rotation, wherein rotation imparted by a motor is transferred to the pipe string so that the pipe string is rotated as well, and wherein the reactive torque is transferred to the pipe string along a path bypassing the motor.
Another embodiment of the invention for achieving this object is formed by a pipe coupling unit for at least coupling or uncoupling a pipe section and a pipe string axially projecting from a rotary drilling rig into a bore hole in the lithosphere. This pipe coupling unit is provided with:
a pipe string engaging structure for engaging the pipe string;
a pipe section engaging structure for engaging the pipe section, the pipe section engaging structure being coaxial with and rotatable relative to the pipe string engaging structure and in a position axially different from the position of the pipe string engaging structure;
a rotationally stationary support structure rotatably supporting the pipe string engaging structure;
a pipe string drive including a drive motor operatively coupled to the pipe string engaging structure and to the rotationally fixed support structure for driving rotation of the pipe string engaging structure relative to the rotationally fixed support structure; and
a pipe section drive for driving rotation of the pipe section engaging structure relative to the pipe string engaging structure with a torque up to a required make-up or breaking torque, which pipe section drive being arranged for transferring a reactive torque in response to the torque up to a required make-up or breaking torque to the pipe string engaging structure along a transfer path bypassing the motor for driving rotation of the pipe string engaging structure.
Thus, the make-up or breaking torque is or can be exerted in a manner which substantially reduces the extent to which the operating equilibrium of the string rotating in the bore hole is disturbed.
According to particular modes of carrying out the invention, the pipe section to be coupled to the pipe string is gradually accelerated to substantially a rotational velocity at which the pipe string is rotating before the make-up or breaking torque is applied and/or before an engaging structure for applying the make-up torque to the pipe section are brought in engagement with the pipe section. Thus disturbances of the operating equilibrium of the rotating pipe section are further reduced.
Further objects, modes, embodiments and details of the invention appear from the dependent claims and the description in which reference is made to the drawings.